Balanced phase detector in automatic frequency control circuit



Sept. 7, 1965 G. w. FYLER ETAL 3,205,453

BALANCED PHASE DETECTOR IN AUTOMATIC FREQUENCY CONTROL CIRCUIT OriginalFiled May l, 1961 2 Sheets-Sheet 1 l George M F7 Zez' dgar HorizontalSept. 7, 1965 Voltage lOO at I4 with Respect to l5 Voltage lOl at 37with Respect to 26 Voltage |02 at 36 with Respect to 29 Voltage |03 atI4 with Respect to Voltage |04 at I4 with Respect to 29 G. W. FYLER ETALBALANCED PHASE DETECTOR IN AUTOMATIC FREQUENCY CONTROL CIRCUIT OriginalFiled May l. 1961 2 Sheets-Sheet. 2

George W Fg e2" United States Patent O 4 claims. (ci. 331-20) Thisapplication is a division of copending application Serial No. 106,859,tiled May 1, 1961. This invention pertains in general to a new andimproved automatic frequency control circuit for controlling theoperating frequency of a television scanning generator. Morespecifically, the invention relates to a novel balanced phase detectorfor controlling the frequency of a transistorized horizontal scanninggenerator.

It is customary to employ in sweep systems for achieving horizontalscanning of television receivers an automatic frequency control (AFC)circuit to insure that precise phase synchronisin is maintained betweenthe received horizontal synchronizing components and the line scanningsignal for the picture tube. Quite often the automatic frequency controlcircuit takes the form of a balanced phase detector which provides acontrol voltage which varies in amplitude and polarity in accordancewith the phase relationship of the instantaneous scanning signals andthe received synchronizing pulses. A balanced type detector is employedto render the system substantially immune to undesired noise signalswhich may be interspersed with the desired synchronizing components.Unfortunately, most, if not all, of the balanced phase detectorsdeveloped to date are actually not precisely balanced due to the natureof their construction, and thus do not achieve the optimum in noiseimmunity. Furthermore, their effectiveness is largely lost where theyare required to operate into finite load impedances.

In accordance with the present invention, a phase detector is providedwhich is accurately balanced. It includes a source of signal pulsesperiodically recurring at a predetermined frequency. There is a firstseries circuit including, in the order named, the pulse signal source, afirst unidirectional device, a source of a first sawtooth shaped signalalso periodically recurring at the predetermined frequency but having aphase relative to the signal pulses which is subject to variation, andone section of a two-section load circuit. A second series circuit isprovided which includes, in the order named, the pulse signal source, asecond unidirectional device, a source of a second sawtooth shapedsignal also periodically recurring at the predetermined frequency andhaving a constant phase relationship with respect to the rst sawtoothshaped signal, and the second section of the load circuit. The first andsecond unidirectional devices are coupled in series opposition acrossthe two-section load circuit. The balanced phase detector of the presentinvention also includes means for developing across the two-section loadcircuit a control signal which varies in accordance with changes in therelative phase of the signal pulses and the sawtooth shaped signals.

The features of this invention which are believed to be new are setforth with particularity in the appended claims. The invention, togetherwith further objects and advantages thereof, may best be understood,however, by reference to the following description in conjunction withthe accompanying drawings in which:

FIGURE 1 is a schematic diagram of a transistorized horizontal sweepsystem for a television receiver which includes an automatic frequencycontrol circuit constructed in accordance with the invention; and,

.ICC

FIGURE 2 comprises signal waveforms helpful in explaining the operationof the AFC circuit of FIGURE 1.

Turning now to a structural description of the scanning system of FIGUREl, the primary winding 10 of a transformer 11 is coupled to a source ofhorizontal or line synchronizing pulses. One side of secondary winding12 of transformer 11 is coupled to a circuit junction or terminal 14 andthe other side of winding 12 is connected to a circuit junction 15.Junction or terminal 14 is connected to the plate or anode of aunidirectional device or diode 16 and also to the plate or anode ofanother unidirectional device or diode 17, the cathode of diode 16 beingconnected in series with a resistor 19 and the parallel combination 18of a resistor 20 and a condenser 21 to circuit junction or terminal 1S.The cathode terminal of diode 17 is similarly coupled in series with aresistor 23 and resistor 24, shunted by a capacitor 25, to circuitjunction 15. For convenience, the parallel combination of resistor 24and condenser 25 is designated network 22.

Connected in parallel with resistor 19 is the series combination of aninductance coil 27 and a secondary winding 28 of a horizontal outputtransformer 30. In the interest of simplifying the drawing, terminalsY-Y of resistor 19 and coil 27 have been shown to indicate a connectionwith corresponding terminals Y-Y of winding 28. Likewise, resistor 23 isshunted by the series combination of an inductance coil 32 and asecondary winding 33 of horizontal output transformer 30, winding 33being interconnected with resistor 23 and coil 32 by means of terminalsX-X. For convenience, the junction of resistor 19, coil 27, and thecathode of diode 16 is designated by the numeral 26. Likewise, thejunction or terminal of resistor 23, coil 32, and the cathode of diode17 is labeled 29.

The series combination of a resistor 34 and a capacitor 35 is coupledbetween the junction 36 of resistor 23, network 22, and the junction 37of resistor 19 and network 18.

All of the circuitry in the drawing discussed thus far collectivelyconstitute an automatic frequency control (AFC) circuit of the balancedphase detector type, and constructed in accordance with the invention,for providing a control signal between terminals 36 and 37 (and thusacross networks 18 and 22 which together constitute a two-section loadcircuit) varying in accordance with changes in the relative phase of thehorizontal synchronizing pulses applied to primary winding 10 and thescanning signals developed in horizontal output transformer 30.Condensers 21 and 25 lter out the horizontal frequency components.

Circuit junction 36 is also connected to the base electrode 39 of a PNPtype transistor 4t). Collector 42 of PNP transistor 40 is connectedthrough a pair of adjustable resistors 44 and 45 to base 39, thejunction of resistors 44 and 45 being coupled through the seriesarrangement of an adjustable resistor 47 and a fixed resistor 46 toemitter 41. Resistors 46 and 47 are shunted by a condenser 4S, and thejunction of those resistors is connected to junction or terminal 37.Transistor 40 presents a resistance between emitter 41 and collector 42,the value of which is determined by the instantaneous amplitude of thecont-rol signal developed across twosection load circuit 18, 22.

Emitter 41 is connected through a secondary winding 49 of a transformer5t) to the base electrode 51 of another PNP Itype transistor 52.Collector electrode 55 of transistor 52 is connected through the primarywinding 56 of transformer Si) to the negative terminal of a source ofunidirectional operating potential, shown as a battery 58, the positiveterminal of which is connected to ground. Emilter 59 of transistor 52 isconnected to the junction of resistors 44, 45 and 47 and also through aload, in the form of an inductance coil 60, to ground. Morespecifically, inductance coil 60 constitutes the primary Winding of atransformer 61. Since the operation of inductance coil 60 is affected bythe circuitry coupled thereto, the term inductive load 60 actuallyrefers to coil 60 plus the resistive circuitry coupled thereto. Load 60comprises the load on transi-stor 52. Base 51 is connected to thenegative terminalof potential source 58 via a resistor 62. Transformer50 has another secondary Winding 63, one terminal of which is connectedto ground and the other (designated 65) of which is connected to thecathode terminal of a unidirectional device or diode 64, the anodeterminal of diode 64 being connected to the negative terminal ofpotential source 58. Inductively coupled to inductance coil 60 is a coil66, one side of which is connected to ground and the other (designated68) to the cathode terminal of a unidirectional device or diode 67, theanode or plate terminal of the diode being connected to the negativeterminal of source 58.

The circuit elements associated with transistor 52 collectively functionas a blocking oscillator, the free running operating frequency of whichis determined in part by .the instantaneous resistance presented betweenemitter 41 and collector 42 of transistor 40. As will be described indetail later, transistor 52 conducts during each trace interval and isturned off during each retrace interval.

A tap 70 of inductive load or primary winding 60 is connected through anadjustable resistor 71, shunted by a capacitor 72, to the base electrode74 of another PNP type transistor 75. Emitter electrode 76 of transistor75 is grounded, while collector 77 of the transistor is coupled to thenegative terminal of potential source 58 by way of a horizontal magneticdeflection yoke 78 and an inductance coil 79 connected in series.Although deflection yoke 78 may have some resistance, with respect tothe horizontal scanning frequency it acts substantially as an inductiveIreactance. The junction 30 of yoke 78 and indue-tance coil 79 isby-passed to ground via a condenser 81. The primary winding 82 ofhorizontal output transformer 30 is connected in shunt with yoke 78. Anadditional winding 84, preferably constituting only a single windingturn, of transformer 30 is connected in series-aiding relationship withprimary winding 82, one terminal of additional winding 84 consequentlybeing connected to high potential terminal 83 of winding 82, while theother termial 87 is connected to the plate or anode terminal of aunidirectional device or damper diode 85, the cathode terminal of whichis connected to ground. A condenser 86 shunts damper 85.

Transistor 75 and the circuitry associated therewith collectivelyconstitute an output stage which, in response to an input drive signalfrom theblocking oscillator, effects the translation of a periodicallyrecurring sawtooth waveform in magnetic deflection yoke 78.

Also connected to primary winding 82 and additional Winding 84 issecondary winding 88, one terminal of which is consequently connected tohigh potential terminal 87 of additional winding 84 and the otherterminal of which is connected to the plate or anode 89 of a highvoltage rectifier tube 90. The cathode filament 91 of rectifier 90 isconnected to another winding 92 of hon'- zontal output transformer 30 inorder to receive heater power. An output connection is provided on oneside of filament-cathode 91 to provide high voltage for the second anodeof a conventional picture tube. It, of course, will be noted that withrespect to windings 82, 84 and 88 output transformer 30 functions as anautotransformer.

In describing the operation of the invention, attention is also directed.to the signal wave forms of FIGURE 2 which appear between variouspoints or terminals in the circuit diagram of FIGURE l. Conventionalhorizontalor line-synchronizing pulses periodically recurring at thehorizontalor line-scanning frequency are derived from the customarysynchronizing signal separator (not shown) and are Iapplied to primarywinding 10 of transformer 11. They appear as positive polarity pulses atterminal 14 with respect to terminal 15 as shown by voltage wave form inFIGURE 4. Of course, each pulse of wave form 100 occurs during a retraceinterval. Meanwhile, ybackV pulses, each of which also occurs during aretrace in-terval of a line-scanning cycle, are developed in windings 28and 33 of horizontal output transformer 30 and are fed back to theautomatic frequency control circuit. Resistor 19 and inductance coil 27constitute an integrating circuit with respect to the flyback pulsesdevel-oped across winding 28, and likewise resistor 23 and inductancecoil32 constitute an integrating circuit for the ilyback pulsesdeveloped in winding 33. As a consequence, sawtooth shaped voltagewaveforms 101 and 102 are developed across resistor 19 and resistor 23,respectively. Waveform 101 is found at terminal 37 relative to .terminal26, and waveform 102 appears at terminal 36 with respect to terminal 29.The phase relationship between these sawtooth voltages is, of course,opposite and constant. Sawtooth shaped signals 101 and 102 which haveamplitudes less than that of the sync pulses across secondary 12,indicate the instantaneous operating frequency of the -scanninggenerator, namely the combination of .the blocking oscillator and outputstage of FIGURE 1.

It will be noted that the balanced phase detector includes two separateseries circuits, one of which includes, in the order named, thesynchronizing pulse signal source, namely secondary winding 12, diode16, the integrating circuit of resistor 19 and coil 27 which constitutea source of sawtooth shaped signal 101, and section 18 of two-sectionload circuit 18, 22. The other series circuit includes, in the ordernamed, pulse signal source 12, diode 17, the integrating circuitincluding resistor 23 and coil 32 which is a source of a sawtooth shapedsignal 102, and a section 22 of two-section load circuit 18, 22. Diodes16 and 17 are thus connected in series opposition across the two-sectionload circuit whereas they are connected in parallel across source 12.Consequently the synchronizing pulses render diodes 16 and 17 conductiveat the same time and effect equal current flow (ignoring the sawtoothvoltage of waveforms 101 and 102) through loads 18 and 22 in thedirection of the arrows. As a result, the sync pulses produce averagevol-tages across resistors 20 and 24 with the polarity shown by the-jand signs, which voltages tend to cancel out across two-section loadcircuit 18, 22, namely between circuit junctions or terminals 36 and 37.Likewise, sawtooth signals 101 and 102 (ignoring the sync components)also tend to produce average current flows through loads 18 and 22 whichcancel out across the two-section load circuit, diode 16 conducting toeffect current llow through load 18 in the direction shown by .theadjacent arrow during the positive portions of voltage waveform 101 anddlode 17 conducting to cause current flow through load 22 in thedirection shown by the adjacent arrow during the positive portions ofvoltage waveform 102. Assuming that the saw-tooth voltages are of thesame amplitude, average voltages are developed across resistors 20 and24 with the polarity shown and cancel out to zero across the entiretwo-sect-ion load section 18, 22.

Considering now the effect of the synchronizing pulses of voltagewaveform 100 on the operation of the balanced phase detector andassuming that the operating frequency of the blocking oscillator and theoutput stage is precisely in synchronism with the frequency of thehorizontal synchronizing pulses, voltage waveform 103 appears betweenterminal 14 and the cathode of diode 16 (junction 26), and voltagewaveform 104 appears between circuit junction 14 and the cathode ofdiode 17 (junction 29). It will be noted that the synchronizingcomponents of waveforms 103 and 104 appear substantially at the midpointof the retrace intervals. Under such circumstances, the average.amplitudes of the vol-tages developed across load circuits 18 and 22are equal and thus both the sawtooth shaped signals and thesynchronizing pulse signals are effectively cancelled out betweenterminals 36 and 37. As .a result, there will be a zero voltagedifference between terminals 36 and 37 which is indicative of operationof the scanning generator precisely at the linescanning frequency.Transistor 40 is normally operated in the middle of its conduction range(namely, Class A), resistor 45 providing a forward bias. Base 39 isconsequently normally slightly negative relative to emitter 41.Resistors 47 and 46 are selected such that their junction is at the samenegative potential as base 39. With this arrangement, when there is azero voltage difference across terminals 36 and 37, transistor 40 stilloperates causing an emitter-collector current flow of a magnituderepresenting operation of the line-scanning generator exactly at thehorizontal sync frequency.

If the frequency of the sawtooth shaped signals 101 and 102 tends todeviate from the frequency of the linesynchronizing components, thephase relationship between the sync pulses and the sawtooth shapedsignals will vary. Assuming, for example, that the scanning generatortends to operate at a faster or higher frequency than the frequency ofthe horizontal syncs, the phase relationship between the sync pulses andthe sawtooth component waveform 103 will vary, the sync pulses occurringsome ltime during the second half of each of the retrace intervals. As aconsequence, the peak voltage of waveform 103 increases while the peakvoltage of waveform 104 decreases, causing an unbalance of the voltagesdeveloped across two-section load circuit 18, 22. Specifically, theaverage voltage developed across section 18 will be greater than thatdeveloped across load 22, which has a net effect of increasing thevoltage difference between emitter 41 and base 39, the base goingnegative with respect to the emitter. This increases theemitter-collector current of transistor 40, causing a decrease in thefrequency of the blocking oscillator.

The automatic frequency control circuit of FIGURE 1 is thus accuratelybalanced and achieves improved immunization against noise disturbances.

The frequency of operation of the blocking oscillator, andconsequentially the frequency of operation of the scanning generator, isdetermined in part by the AFC control signal developed across twosectionload circuit 18, 22. Resistors 44, 45, 46 and 47 also affect theblocking oscillator frequency. Adjusting resistor 45 varies theoperating point of transistor 40, resistor 44 determines the range ofoperation, and .the adjustment of resistor 47 varies the frequency ofthe blocking oscillator. Since the emitter-collector path of transistor40 is in ser-ies with the base-emitter circuit of blocking oscillatortransistor 52, the ampli-tude and Ipolarity of the AFC control voltageapplied to the base-emitter junction of transistor 40 will determine, inpart, the magnitude of the base input drive current for transistor 52.This follows because the resi-stance between emitter 41 and collector 42varies with variations in the AFC control voltage.

Transistor 52 is normally forward biased by virtue of the connection ofbase 51 to the negative terminal of operating potential source 58 viaresistor 62, emitter 59 being at ground potential. When the system isinitially placed into operation, transistor 52 is turned on, like aswitch, as a result of the forward bias provided by potential source -orbattery 58 and a trace interval is started. At that time, .the amount ofbase drive current fiowing through the base-emitter path of transistor52 is more than enough to maintain the transistor in a saturatedcondition. This effects current translation through the series circuitincluding inductive yload or primary winding 60, the emitter-collectorpath of transistor 52 and primary winding 56 of transistor 50 to thenegative terminal of potential source 58.

However, `due to the fact that the collector load, including primary 56and primary 60, is largely inductive, the emitter-collector current oftransistor 52 is not permitted to increase instantaneously but insteadincreases in sawtooth fashion. The increasing current in primary winding56 induces a voltage in secondary winding 49, the negative polarityterminal of which is that connected to base 51 in order to maintaintransistor 52 conductive.

Inasmuch as inductive load 60, which as mentioned before actuallyincludes the circuitry coupled thereto, has a resistive component, .theemitter-collector current of transistor 52 does not increase completelylinearly. The time rate of change of current through primary winding 56therefore decreases while the emitter-collector current is increasing.Consequently, the voltage induced in Winding 49 decreases with aresultant decreasing base drive current. The emitter-collector currentincreases until the decreasing base drive current reaches the point atwhich transistor 52 no longer is saturated. At that instant, the rise incollector current ceases and the magnetic field of primary 56 collapsesto induce a voltage in secondary winding 49 of a positive pola-rity atthe terminal adjacent base 51 to reverse bias .the base-emitter junctionof transistor 52, cutting it off rapidly. The cutting off process isaided by the customary regenerative action typical in blockingoscillators.

Transistor 52 is maintained in its off condition during an interval,which of course is the retrace time, determined primarily by theconstruction of transformer 50. The positive voltage across winding 49must terminate before transistor 52 becomes forward biased again toinitiate another cycle of operation in the same manner as described.

As is well known, changing .the base drive current, which occurs byvarying the resistance between emitter 41 and collector 42 of transistor40, changes the saturation point of transistor 52 yand thus changes thefrequency of operation of the blocking oscillator. For example,decreasing the base drive current 'lowers the saturation point and thusdecreases the trace time. A more detailed explanation of the oper-ation`of the blocking oscillator may be found in the aforementioned copendingapplication Serial No. 106,859.

The voltage at emitter 59 with -respect to ground increases negatively=during each trace interval because of the increasing emitter-collectorcurrent of transistor 52. The voltage across inductive load 60 issubstantially proportional to the increasing collector currentmultiplied by .the reflected or transferred load resistance of thebaseemitter circuit of transistor 75. During each trace interval,inductive energy is stored in the magnetic field of inductive load 60.Relatively high amplitude positive going pulses occur dur-ing retrace4at emitter 59 with respect .to ground as a result of the energy builtup and stored in inductive load 60 yduring each trace interval.

Output transistor in a sense is operated in a similar fashion astransistor l52, in that it basically serves as a switch, being turned onor rendered conductive during each -tr-ace interval, and is turned olfor rendered nonconductive during each retrace interval. Driving oftransistor 75 in such a manner is achieved by the voltage developed atemitter 59. As described in detail in copending application Serial No.106,859, the output stage effects the development in magnetic deflectionyoke 78 of a scanning current having -a periodically recurring sawtoothwaveshape.

While a particular embodiment of the invention has been shown anddescribed, modifications may be made, and it is 4intended in the.appended claims to cover all such modifications as may fall within thetrue spirit and scope `of the invention.

We claim:

1. A balanced phase detector comprising: a source of signal pulsesperiodically recurring at a predetermined frequency, said source havingfirst and second output terminals;

a load circuit including two series-connected load sections having acommon terminal;

a first series circuit including, in the order named, said pulse signalsource, a first unidirectional device directly connected to said firstoutput terminal of said pulse signal source, a source of a firstsawtooth shaped signal also periodically recurring at said predeterminedfrequency, but having a phase relative to said signal pulses which issubject to variation, and one section of said load circuit with saidcommon terminal thereof directly connected to said sec- Iond outputterminal of said pulse signal source;

a second lseries circuit including, in the order named, said pulsesignal source, a second unidirectional device directly connected to saidfirst output terminal, Ia source of a second sawtooth shaped signal alsoperiodically recurring at said predetermined frequency and having aconstant phase relationship with respect to said first sawtooth shapedsignal, and the second section of said load circuit, said first andsecond unidirectional devices connected in series opposition across saidtwo-section load circuit;

and means for developing aiross said two-section load circuit a controlsignal which varies in accordance with changes in the relative phase ofsaid signal pulses and said sawtooth shaped signals.

2. A balanced phase detector comprising: a load circuit including twoseries-connected load sections;

first and second unidirectional devices connected in series oppositionacross said load circuit;

a source Iof signal pulses periodically recurring at a predeterminedfrequency;

means for connecting said unidirectional devices in parallel 4acrosssaid pulse signal source;

a source of first sawtooth shaped signal also periodically recurring atsaid predetermined frequency;

means for coupling said first saw tooth shaped signal source in serieswith said first unidirectional device, .said pulse signal source and onesection of said load circuit;

a source of a second sawtooth shaped signal also periodically recurringat said predetermined frequency and having a constant phaserelation-ship with respect to said first sawtooth shaped signal;

means for coupling said second sawtooth shaped signal source in serieswith said second unidirectional device, said pulse signal source and theother section of lsaid two-section load circuit, the amplitude andpolarity of said first and second .sawtooth shaped signals being suchthat said sawtooth shaped signals tend to cancel out across saidtwo-section load circuit, whereas said signal pulses tend to cancel outonly if a predetermined' phase relationship exists between said signalpulses and said sawtooth shaped signals.

and means for developing -across said two-section load circuit a controlsignal which varies in accordance with changes in the relative phase ofsaid signal pulses and said sawtooth -shaped signals.

3. An automatic frequency control circuit comprising:

a source of synchronizing pulses periodically recurring at apredetermined frequency, said source having first and second outputterminals;

a load circuit including two series-connected load sections having acommon terminal;

a first series circuit including, in the order named, said synchronizingpulse source, a first unidirectional device directly connected to saidrst output terminal of said synchronizing pulse source, a firstintegrating circuit, and one section of said load circuit with saidcommon terminal thereof connected to said second output terminal of saidsynchronizing pulse source;

a second series circuit including, in the order named,

said synchronizing pulse source, a second unidirec- 8 tional devicedirectly connected to said first output terminal, a second integratingcircuit, and the second section of said load circuit, said first andsecond unidirectional devices connected in series opposition across saidtwo-section load circuit;

ia scanning generator;

means for simultaneously developing in said scanning generator a pair offeedback signals each of which contains a series of pulses recurring atthe instantaneous frequency of said scanning generator;

means for applying said pair of feedback signals to said first andsecond integrating circuits respectively to produce first and secondsawtooth shaped signals having average amplitudes and polarities tendingto cancel out across said two-section load circuit, said synchronizingpulses tending to cancel out across said load circuit only if apredetermined phase relationship exists between said synchronizingpulses land said sawtooth shaped signals indicative of operation of saidscanning generator at said predetermined frequency;

means for developing across said two-section load circuit a controlsignal which varies in amplitude any time the frequency of operation ofsaid scanning generator deviates from said predetermined frequency; andmeans for utilizing said control signal to control the operatingfrequency of said scanning generator.

4. An automatic frequency control circuit comprising:

a source of horizontal synchronizing pulses periodically recurring at apredetermined frequency, said source having first and second outputterminals;

a load circuit including two series-connected load sections having acommon terminal;

a first yseries circuit including, in the order named, saidsynchronizing pulse source, a first unidirectional device directlyconnected to said first output terminal of said synchronizing pulsesource, a first integrating circuit including a resistor and aninductance coil, :and one section of said load circuit with said cornmonterminal thereof directly connected to said second output terminal ofsaid synchronizing pulse source;

a second series circuit including, in the o rder named,

.said synchronizing pulse source, a -secorid unidirectional device,directly connected to said first output terminal, a second integratingcircuit including a resistor and an inductance coil, and the secondsection of said load circuit, said first land second unidirectionaldevices connected in series opposition across said two-section loadcircuit;

a transistorized horizontal scanning generator;

means for simultaneously developing in said scanning generator a pair offeedback signals each of which contains a series of pulses recurring at`the instantaneous frequency of said horizontal scanning generator;

means for applying said pair of feedback signals to said first .andsecond integrating circuits respectively to produce first and secondsawtooth shaped signals having average amplitudes and polarities tendingto cancel out across said two-section load circuit, said horizontalsynchronizing pulses tending to cancel out across said load circuit onlyif a predetermined phase relationship exists between lsaid synchronizingpulses and said sawtooth shaped signals indicative of operation of saidscanning generator at said predetermined frequency;

means for developing across said two-section load circuit a controlsignal which varies in amplitude anytime the frequency of operation ofsaid horizontal scanning generator deviates from said predeterminedfrequency; and means for utilizing said control sig- 9 10 nal to controlthe operating frequency of said scan- 3,029,391 4/ 62 Fyler 331-26 Xning generator. 3,061,674 10/62 Janssen et yal. 178-69.5 3,070,657 12/62Shimada 331-20 X References Cited by the Examiner UNITED STATES PATENTS2,742,591 4/56 Procter 331-20 X 5 ROY LAKE, Primary Examiner.

JOHN KOMINSKI, Examiner.

1. A BALANCED PHASE DETECTOR COMPRISING: A SOURCE OF SIGNAL PULSESPERIODICALLY RECURRING AT A PREDETERMINED FREQUENCY, SAID SOURCE HAVINGFIRST AND SECOND PUTPUT TERMINALS; A LOAD CIRCUIT INCLUDING TWOSERIES-CONNECTED LOAD SECTIONS HAVING A COMMON TERMINAL; A FIRST SERIESCIRCUIT INCLUDING, IN THE ORDER NAMED, SAID PULSE SIGNAL SOURCE, A FIRSTUNIDIRECTIONAL DEVICE DIRECTLY CONNECTED TO SAID FIRST OUTPUT TERMINALOF SAID PULSE SIGNAL SOURCE, A SOURCE OF A FIRST SAWTOOTH SHAPED SIGNALALSO PERIODICALLY RECURRING AT SAID PREDETERMINED FREQUENCY, BUT HAVINGA PHASE RELATIVE TO SAID SIGNAL PULSES WHICH IS SUBJECT TO VARIATION,AND ONE SECTION OF SAID LOAD CIRCUIT WITH SAID COMMON TERMINAL THEREOFFDIRECTLY CONNECTED TO SAID SECOND OUTPUT TERMINAL OF SAID PULSE SIGNALSOURCE; A SECOND SERIES CIRCUIT INCLUDING, IN THE ORDR NAMED SAID PULSESIGNAL SOURCE, A SECOND UNIDIRECTIONAL DEVICE DIRECTLY CONNECTED TO SAIDFIRST OUTPUT TERMINAL, A SOURCE OF A SECOND SAWTOOTH SHAPED SIGNAL ALSOPERIODICLLY RECURRING AT SAID PREDETERMINED FREQUENCY AND HAVING ACONSTANT PHASE RELATIONSHIP WITH RESPECT TO SAID FIRST SAWTOOTH SHAPEDSIGNAL, AND THE SECOND SECTION OF SAID LOAD CIRCUIT, SAID FIRST ANDSECOND UNIDIRECTIONAL DEVICES CONNECTED IN SERIES OPPOSITION ACROSS SAIDTWO-SECTION LOAD CIRCUIT; AND MEANS FOR DEVELOPING AIROSS SAIDTWO-SECTION LOAD CIRCUIT A CONTROL SIGNAL WHICH VARIES IN ACCORDANCEWITH CHANGES IN THE RELATIVE PHASE OF SAID SIGNAL PULSES AND SAIDSAWTOOTH SHAPED SIGNALS.